Continuous casting and rolling systems for non-ferrous metals, including copper, have been known for many years. These continuous rod production systems generally include apparatus for providing a continuous stream of molten metal to a casting machine in which the metal is solidified as a continuous cast bar, then passed through an in-line continuous rolling mill, an in-line rod cleaning apparatus, and a coiling machine where the finished rod product is collected for transport to further processing stations or for shipment.
The copper rod systems pioneered by the assignee of this invention initially produced copper rod at a production rate of about 10 tons per hour, and now produce higher-quality rod at much greater capacities. The success of such systems is based on the vastly improved copper rod product produced thereby and on the economic advantages resulting from the continuous nature of the rod production process. Similar continuous rod systems are available for other non-ferrous products, such as aluminum and aluminum alloy rod, as well as for ferrous products. Because manufacturing economies are related to system speed improvements, production rate limitations of any of the system elements limits further improvements in the economy of the system as a whole; thus high-productivity system elements are more desirable. However, handling of the very rapidly advancing rod produced by such systems may introduce undesirable product qualities, e.g., from work hardening and/or plastic deformation of the product.
Referring to FIGS. 1-5 there is shown an example of a conventional continuous metal casting and rolling system 10, in which molten metal is supplied by a melting means 11 to a pouring means 14, poured into a mold comprising a peripheral groove in a rotating casting wheel 12 and a casting band 13 which covers a portion of the casting wheel periphery to form a continuously advancing mold. Coolant is applied to the closed portion of the moving mold to solidify the molten metal, forming a continuously cast bar 15, which is guided away from the casting machine by a cast bar conveyer 16 and directed to subsequent operations. A shear 17 is used to sever sections of the cast bar 15, as may be required during manufacturing operations. The cast bar 15 may be routed through pre-rolling station 18 which may comprise an initial bar treatment apparatus. The cast bar is then directed into rolling mill 19, in which a plurality of roll stations work the cast bar, reducing its cross sectional area and elongating it to form a continuously advancing rod product 22. A delivery pipe 20 (see also FIG. 2) in which cooling, thermal, and/or chemical treatments may be performed, guides the continuously cast and rolled rod product 22 to a turndown 54 and thence into a coiler station 21, where the rod is collected into coils 23 for convenient handling and storage or shipment.
An early arrangement of the coiler station 21 is shown in FIG. 2. From rolling mill 19 the rod product is directed to a pair of pinch rolls 24 via a pathway such as delivery pipe 20. From the pinch rolls 24, the rod 22 is directed from horizontal axis 40 through turndown feed tube 54 to a vertical axis 32 downwardly into a flyer tube 31 from which it is laid into coils in a known manner.
A rollerized guide described in U.S. Pat. No. 4,068,705 is shown in FIGS. 3 and 4 hereof. The rod 22 in such apparatus passes into a guide mechanism 25 which functions to guide the rod from a substantially horizontal direction of movement along axis 40 toward a substantially vertical direction of movement along axis 32. As shown in FIG. 4 hereof, rod guide mechanism 25 includes a pair of arcuate side plates 215 and 216 which support a series of spaced apart rollers 218a, 218b, 218c, etc., and an arcuate rod conduit 219. Arcuate rod conduit 219 is generally tubular and includes a series of spaced slots 220 along its upper convex surface. Rollers 218a, etc. are supported by arcuate side plates 215 and 216 so that their peripheries extend into slots 220. The rod passing through rod conduit 219 normally would engage the concave surface of the rod conduit 219; however, rollers 218a, etc., function to hold the rod away from the surface of rod conduit 219, and isolate the rod from the sliding friction it normally would encounter when it engages the surface of rod conduit 219. Rollers 218a, etc., are mounted on ball bearings and are relatively friction-free. Thus, the rod passing through rod guide mechanism 25 is directed through a 90.degree. arc with a minimum of friction.
Rollers 218 are spaced at approximately 10.degree. intervals from each other through the 90.degree. arc defined by the rod guide mechanism 25. This close spacing of the rollers is such that the initial leading end of the rod passing through the system will normally not engage the surface of rod conduit 219 of rod guide mechanism 25, but will be positively guided in a downward direction by the rollers.
Entrance guide tube 221 is connected to arcuate rod conduit 219 along rod path 40. The end 222 of entrance guide tube 221 may be flared outwardly to receive the leading end of the rod passing along path 40 and guide the rod into rod guide mechanism 25. Similarly, exit guide tube 224 is positioned adjacent the vertical end of rod guide mechanism 25, and includes a flared end 225 which receives the rod from rod guide mechanism 25. Exit guide tube 224 guides the rod 22 in a vertical direction along axis 32 toward, for example, a coiler below.
A portion of an improved rollerized turndown 35 similar to that described in U.S. Pat. No. 4,944,469 is shown in FIG. 5, wherein a plurality of freely rotatable roll pairs, such as roll pair 33, 34, guide the rod 22 from pinch roll 24 down to the coiler 21 along vertical axis 32. This arrangement may include a second pinch roll pair 26 arranged along the vertical axis 32.
It is believed that ferrous rod may undergo a similar horizontal-to-vertical transition in certain other rod rolling mill installations, wherein, after rolling, the rod is passed around a large rotating wheel. This is illustrated generally in FIG. 6. The wheel 300 includes an exit pinch roll 304 for retaining the rod 22 in contact with the wheel 300. It is also believed that in certain rolled rod installations, a V-grooved wheel may be used for a similar purpose, and may include an exit pinch roll 304 to ensure contact of the advancing rod with the wheel.
Rod pinch rolls, such as the pinch rolls 24 shown in FIGS. 2 and 5, are used to pull finished rod from a rod mill and to assist in conveying the rod to the next in-line station, such as a coiler. A certain amount of pulling force is required to pull, or to push, the rod. This pulling force is produced by a coefficient of friction between the rod and the pinch roll surface multiplied by the force normal to the rod. In the case of a relatively soft material, such as copper, the force normal to the rod may be enough to deform the rod, thereby working the soft metal, and thus raising the yield strength of the rod. An increase of yield strength may be detrimental to the subsequent operations performed on rod, such as drawing the rod into wire, and is preferably avoided.
It has been determined that the coiled rod product made according to the above-described prior art apparatus has a substantially greater yield strength than the as-rolled rod product, especially in high speed rod systems which require substantially greater pinch roll pressure. While this is normally acceptable for most applications, in certain instances, it would be desirable if the yield strength were maintained at or near that existing as the rod exits the rolling mill and is cooled.
Hot "dead soft" copper rod exiting the rolling mill, if cooled and unworked, exhibits a yield strength below about 10,000 pounds per square inch (psi), which may be more desirable in certain subsequent manufacturing operations. It is therefore desirable to minimize unnecessary increases in yield strength during the rod processing operations.
It has been determined that the coiled continuous cast and rolled rod product from the prior art apparatus normally exhibits a tensile yield strength of about 17,000 to about 20,000 psi, while it is known that unworked, unhardened, or "dead soft" copper rod exhibits a tensile yield strength of about 8,000 to about 10,000 psi after exiting the rod mill at about 1100.degree. F. and then cooled. The cause of the increased yield strength is work hardening and/or plastic deformation of the hot rod product that occurs in the pinch rolls and turndown portion of the apparatus.